The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:

A dealer may encounter a customer concern of the SES light on, a Glow Plug Control Module (GPCM) DTC, or individual cylinder glow plug DTCs. A loose battery feed connection at the battery, starter, alternator, or the Glow Plug Control Module (GPCM) may induce glow plug concerns.

This PI will describe and assist with concerns related to GPCM and/or Glow Plug DTCs.

Recommendation/Instructions:

The first portion of this PI will discuss GPCM diagnostics and repairs.

If a vehicle has been brought in with GPCM concerns or DTC P064C the GPCM battery positive cable will need to be inspected. Inspect for loose connections at the GPCM Connector (squeeze type terminal number C1 or X1) and at the power source/mega fuse. If the squeeze type terminal is damaged, the complete cable would need replaced. If the GPCM terminal is damaged, the GPCM would need replaced. Retorque loose mega fuse/power source connections using current SI specifications.

Note: The source or main power feed to the GPCM differs depending on the vehicle being serviced. Use the current SI power feed distribution schematics for power feed location.

If a 2007-2008 GMT900 C/K truck has DTC P064C, and both ends of the main power feed terminal have been inspected it's possible to have a cable crimping concern. The crimp may not make a positive connection, and will not be easily detected. If necessary replace the GPCM Battery Positive Cable on 2007-2008 GMT900 C/K trucks.

Evaluate DTC P064C after connections are inspected and repaired. Complete the following steps twice to see if P064C resets.

Start engine; let the engine run for at least 2 minutes, ignition off for at least 2 minutes, restart engine to verify P064C has not returned. If P064C resets after all connections have been repaired (GPCM has NOT been replaced yet) replace the GPCM.

This section of the PI discusses Glow Plug diagnostics and repairs.

Glow plug DTCs P0671-P0678 may be caused by internal opens in the glow plugs. There are two different descriptions for an open in a glow plug. A fast open glow plug is a plug with an internal open circuitry, with no visual damage to the tip of the plug. A slow open glow plug is a plug that has internal open circuitry, and the tip of the plug is missing or damaged.

If the diagnostics for P0671-P0678 led to a glow plug resistance of more than 1 ohm, replace all of the glow plugs. If any of the glow plug tips are missing, the cylinder head must be removed. All debris must be removed from the cylinder. When the tip of a glow plug enters the cylinder, engine damage may occur. Make any engine mechanical repairs as needed.

There are certain electrical concerns that may induce the glow plug to go open. If the glow plug system senses a certain electrical "noise" on the power feed, it could induce glow plug concerns. This electrical "noise" may be induced by jump starting, loose connections, disconnecting the batteries with the ignition in the ON position, or a battery charger being used during a module reprogramming event.

Complete all electrical circuit inspections and engine repairs as described. On 2006 model year vehicles be sure the updated calibration was installed into the GPCM per Campaign 06522. After installing the new GPCM software, complete the Fuel Injector Flow Rate Programming following SI procedures.

Note: Do not replace the GPCM for any one or combination of the following internal open glow plug codes: P0671, P0672, P0673, P0674, P0675, P0676, P0677 or P0678 when not accompanied by GPCM Diagnostic Trouble Codes. GPCMs have been returned and inspected with no problem found.

Note: Aftermarket Add-on remote starter or alarm kits must be removed before any glow plugs are replaced. Interruptions to normal starting procedures may induce glowplug concerns.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

Mine goes in tomorrow. Just started having problems. Will have to see what's affected. My question is that I have a 'tune' put in by Nick from Duramax tuner. Will that new software take out my tune?

Jim

What new software? The glow plug module campaign/recall? If so that just reflashes the Glow plug control module, then the injector flow rate data is copied from the ECM to the GPCM. I'd say no, you shouldn't lose it.

I had the #3 go out on my in August at 66k miles. Replaced all 8 with AC Delco parts for $128 and a couple hours of time. It was worth $28 to not have to deal with the trip to/from the dealer plus the shuttle.

I had 7 that still tested between 0.5 and 0.6 ohms, and the bad one tested at around 200 ohms. I noticed that there was significantly more corrosion on the terminal stud of the bad one compared to the others. I'm wondering if anyone else is seeing a little bit of corrosion causing theirs to go out as well. I imagine corrosion on one would cause more or less current to go through just one causing premature failure?

The passenger side ones are all a piece of cake to change. The drivers side ones are a little more difficult to change with the turbo hose and steering shaft in the way.

I had one go bad last winter on my LBZ at about 65K and the dealer did all 8 for the $100 ded. It seemed like A LOT of talk of these last winter. I'm guessing it will continue this winter and maybe even get worse... possibly turning into an "epidemic" amongst our otherwise bulletproof trucks.

It's nice to see GM step up and take care of it for minimal $$.

Just a note to those thinking of doing it themselves... when I read up on it there were a few people who broke plugs when changing them which turns into a real headache. To me the $100 was well worth it to let the dealer take the risk.

Truck is at Dealer getting 8 new glow plugs and will be ready this afternoon. Service Manager said they were seeing quite a few of these in the 2006 trucks -he didn't elaborate much on specifics. Not sure if they will try to collect the $100 or not at this point but the 2006 Warranty Book is clear 5/50,000 Federal Emissions Warranty then 5/100k Duramax Engine Warranty.

Got truck back last night -8 new glow plugs installed under the 5/50000 Fed Emissions Warranty so no out of pocket expense. Just barely under the 50K mileage limit. Over 50K the repair falls under the 5/100K Duramax engine warranty with the deductable.

FYI to everybody. Service Manager said almost all engine related warranty repairs require an ECM OS Calibration snap shot to get warranty authorization.....

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